Described herein is a method for detecting activation of an operator control element in a motor vehicle. Also described herein is a control device and a motor vehicle having the control device.
The operator control element may be a pushbutton, for example. If such an operator control element is activated by a user of the motor vehicle, this can activate a vehicle function, that is to say can initiate an action. The pushbutton signal is read in and evaluated by a control device for the purpose of detecting the activation. So-called ground switches are often used in operator control elements, that is to say a signal input of the control device is electrically connected or short-circuited to a ground potential when the operator control element is activated. If the control device detects a voltage dip at the signal input, that is to say a voltage value less than a predetermined threshold value is at the control input, the control device identifies the operator control element as activated.
The disadvantage of this activation detection is that the control device is dependent on a stable temporal profile of a supply voltage for the control device and for the operator control element. However, an unstable supply voltage may arise in a motor vehicle, that is to say the supply voltage may fall to a value less than a predetermined nominal value irrespective of activation of the operator control element, which then also results in a decrease in the voltage at the signal input of the control device. For example, the disconnection and connection of the vehicle battery may cause a high degree of ripple in the vehicle electrical system, that is to say voltage fluctuations of the supply voltage. This may result in the voltage at the signal input of the control device dipping greatly. The control device would then incorrectly detect activation of the operator control element.
Brief voltage fluctuations are generally already prevented by the debounce time, that is to say the activation signal from the operator control element must be applied to the signal input of the control device for a predetermined minimum signal duration, namely the debounce time, before the control device actually signals the activation. The debounce time therefore specifies for how long the activation signal must at least be applied before the control device signals the activation. The more robust the signal input is intended to be, the greater the selected debounce time. In order to also compensate for voltage fluctuations which arise when disconnecting or connecting the battery or when operating the electrical starter for an internal combustion engine of the motor vehicle, an undesirably high debounce time must be set. Although the system is then safe from such voltage fluctuations, the reaction time becomes large as a result. If the user of the motor vehicle activates the operator control element for a very short time, for example taps on a pushbutton for an excessively short time, activation is not detected because the debounce time has not yet expired before the activation signal has ended again.
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